In a related art, there has been an electric device formed by covering an electrode stack (a layered electrode unit) with a laminate sheet that is an outer packaging member. The electrode stack is formed by arranging positive and negative electrodes in layers through a separator.
From the viewpoint of productivity of the electric device, a bagged electrode (or a packaged electrode) obtained by packaging one of the positive and negative electrodes in a pair of separators is widely used. For instance, the bagged electrode obtained by packaging the positive electrode in the pair of separators and the negative electrode are alternately arranged in layers, then the electrode stack is formed.
Here, the bagged electrode is formed not by welding the whole circumference of the separator along four sides of the separator, but, in general, by partly welding the four sides of the separator (for instance, see Patent Document 1).